Neutralization of alkyl pyridinium chlorides



Patented Apr. 4, 1950 N EU'IRALIZATION 0F ALKYL PYRIDINIUM CHLORIDES Lawrence A. Dirnberger, Berea, Ohio, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application September 30, 1947, Serial No. 776,896

1 Claim.

This invention relates to a process for making neutral alkyl pyridinium chlorides, and relates more particularly to a process for production of alkyl pyridinium chlorides in which trisodium phosphate is used for neutralization of acidic solutions containing alkyl pyridinium chlorides. This invention further relates to the alkyl pyridinium chlorides so produced.

Known processes for the manufacture of neutral alkyl pyridinium chlorides are inadequate, and the products are unsatisfactory. When caustic soda is used for neutralization, alkyl pyridinium chlorides are highly alkaline and undergo considerable pI-I variation on standing. The alkalinity causes substantial blackening of product. In addition, the manufacturing process is diiiicult to control. The process is expensive because large quantities of decolorizing `agent are required for treatment of the discolored product.

It is an object of this invention to provide neutral alkyl pyridinium chlorides of good color, purity, and pI-I stability. It is afurther object of this invention to provide an easily-controlled process for making neutral alkyl pyridinium chlorides of high quality. Other objects will appear hereinafter.

The foregoing and other objects are attained by using trisodium phosphate as a neutralizing agent. With the use of trisodium phosphate, there is no rapid increase of pI-I of solution, there is little discoloration, and the process is readily controlled. A product of enhanced pI-I stability With a relatively low metal-ion content is obtained.

The phosphate neutralization is performed in ordinary operating equipment. In a batch-type operation, the proper quantity of phosphate is merely poured into the container while the acidic solution is agitated. In a continuous-type operation, the phosphate may be added by piping in a continuous stream. The neutralization may conveniently be terminated at the desired pH, as slight excesses of trisodium phosphate increase the pI-I of the solution very little.

While the phosphate reaction may be employed for neutralization of any alkyl pyridinium chloride, it is of particular interest in the neutralization of Lorol pyridinium chloride. Lorol pyridinium chloride substantially comprises a mixture of straight-chain normal alkyl pyridinium chlorides whose alkyl groups contain an even number of carbon atoms in the range of to 18. For example, the Lorol group is a mixture containing the decyl, dodecyl, tetradecyl,

hexadecyl, and octadecyl groups in varying quantities. A large proportion of Lorol pyridinium chloride comprises dodecyl pyridinium chloride. The average chain length in the Lorol group approximates 13.2 carbon atoms.

In the manufacture of Lorol pyridinium chloride, the crude materials are pyridine and Lorol chloride. A mixture comprising approximately 2 mols of pyridine per mol of Lorol chloride is placed in a reaction tank. The temperatrue is elevated and the reaction proceeds to a yield of approximately 75%. The mixture is then heated to distill out excess pyridine. The high distillation temperature causes a partial decomposition of unreacted Lorol chloride, and releases small quantities of hydrochloric acid and unsaturated hydrocarbons such as dodecene. As a result, subsequent dilution of the reaction mass forms an acidic solution. The acidity is neutralized by addition of measured amounts of trisodium phosphate. The neutralization process may be completed in one step or it may be interrupted While the solution is still acidic, so that further purication may be employed before the solution is completely neutral. In any event, after nal neutralization, the pI-I of the product remains constant at approximately '7.0. Experimental results show that caustic-neutralized Lorol pyridinium chloride exhibits a pH variation as high as 1.5 per month of standing, While the maximum variation in trisodium phosphateneutralized product is 0.1 pI-I. Many samples of the trisodium phosphate-neutralized material show practically no pI-I variation.

While the manufacture of neutral Lorol pyridinium chloride, using trisodium phosphate, may be carried out in diiierent Ways, and may be varied to iit the available equipment, it is a preferred embodiment of this invention to perform the operation in accordance with the example which is depicted on the appended ow sheet.

In step 1, Lorol chloride and pyridine are reluxed with agitation at a temperature of 245 to 275 F. for a period of about seven hours. In this step, the principal reaction takes place.

In step 2, the temperature is increased to approximately 350 F. for three hours, and the excess pyridine is distilled off and is recovered by condensation for recycling in the process. The high temperatures in this step cause partial decomposition of Lorol chloride, and the mix becomes acidic.

In step 3, the mixture is agitated by intimate contact with saturated steam in order to remove residual pyridine and Lorol chloride. This 3 sparging step continues for approximately three hours.

In step 4, the mix is diluted to a strength of about 45% by straight addition of Water.

In step 5, activated carbon of the type ordinarily used for absorbing solids is added. It is effective in decolorizing the solution, and also absorbs metallic nion impurities. The mixture is agitated for about 45 minutes.

In step G, the acidic solution is neutralized by addition of controlled amounts of trisodium phosphate. A technical grade of trisodium phosphate is sufliciently pure. The trisodium phosphate addition is stopped when the solutionreaches a pH of approximately 5. Trisodium plfios'pl'iate.also

`in the form .of pyridine hydrochloride, but was liberated by the partial neutralization in step 6.

In step 8, a diatomaceous earth filter aid is added and the solution is filtered in order to remove insoluble impurities. vIrnpurities adsorbed on the activated carbon are also removed.

In step 9, a fresh charge of activated carbon is added. The mixture is agitated for about 45 minutes.

In step 10, the solution is completely neutralized by addition of trisodium phosphate. The step is carried out in a manner similar to step 6, and trisodium phosphate addition is stopped at va pH between,6.5 and 7.5, and preferably at 7.0. When trisodium phosphate is used, there is little danger of obtaining a highly alkaline solution.

Addition of a excess of trisodium phosphate produces a pH oonly '7.3.

The low `pI-I obtained by using trisodium phosphate is advantageous in several ways. The ex- 1 tent of discoloration appears to depend upon pH,

ing equipment. For example, a bricklined sparge kettle may be employed for all sparging operations, since it is not corroded by acid solutions.

In step 11, the solution is again sparged with steam for removal of objectionable odor.

In step 12, a diatomaceous earth lter aid is added and the solution is filtered in order to re- :lriove impurities adsorbedon theY activated carkIn step 13, the pH of the puriiied Lorol pyridium chloride is adjusted by addition of tri sodium phosphateor phosphoric acid. The product is a viscous light-colored solution, relatively free from odor. The concentration of the solution may be adjusted as desired. The stable neutrality of the phosphate-neutralized material also widens the field of application in packaging.

The solution may be concentrated by vacuum drying, and neutral Lorol pyridine chloride may be cast in solid form.

I claim:

In a process for making purified neutral dodecyl pyridinium chloride from dodecyl chloride and pyridine, the steps comprising treating a crude acidic dodecyl pyridinium chloride solution with activated carbon for decolorizing and removing impurities, adding trisodium phosphate until the pH of the solution is 4.5-5.5, sparging with steam, filtering to remove activated carbon and impurities, agtating the filtrate with activated carbon, adding trisodium phosphate until the pH of the solution is 6.5-7.5, spar'ging with steam, and ltering.

LAWRENCE A. DIRNBERGER.

REFERENCES CITED The vfollowing references are yof record in the file-of this patent:

UNITED STATES PATENTS Number vName Date Y 1,966,334 Ernst May 29, 1934 2,050,924 DeGroote Aug. 11, 1936 2,449,274 `Broll Sept. 14, 1948 FOREIGN PATENTS Number Country Date 379,396 Great Britain 1932 OTHER REWRENCES Clarke, The Urologie & Cutaneous Review, pp. 245-246, Sept. 1, 1942.

Epstein, Oil and Soap, Sept. 1943, pp. 171-174. 

